The disclosure of Japanese Patent Application No. 2000-151891 filed on May 23, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to a vehicle drive apparatus equipped with a power transfer apparatus that includes a transmission mechanism that performs speed shift operation via an operating fluid supplied from a pump driven by a driving motor, and a control method of the vehicle drive apparatus.
2. Description of Related Art
A transmission mechanism is known in which a belt is disposed on two pulleys on input and output sides, and the effective radii of the pulleys are variable in accordance with the positions of engagement of the belt on the pulleys. If the belt-contacting surfaces of the pulleys have the shape of the peripheral surface of a cone or a portion thereof, the value of the effective radius of each pulley can be continuously varied, and therefore, a transmission mechanism of continuously variable speed ratio can be provided.
A related art of a vehicular power transfer mechanism incorporating such a transmission mechanism is described in Japanese Patent Application Laid-Open No. HEI 1-193453. In an apparatus described in this patent application, each of two pulleys is made up of two sheaves generally having the shape of a cone or a truncated cone. These sheaves are disposed with their conical peripheral surfaces facing each other. A belt is clamped between the peripheral surfaces of the sheaves. By changing the interval of the sheaves of each pulley, the radius of the belt-engaged position can be changed. By controlling the sheave interval of the input and output-side pulleys, the belt-engaged positions on the pulleys can be controlled so as to control the ratio between the rotation speeds of the input and output pulleys, that is, the speed ratio.
The interval between the two sheaves is changed by moving one of the sheaves via a hydropneumatic actuator. In order to maintain the sheave position despite reaction force from the belt, it is necessary to supply operating fluid at a predetermined pressure.
If the supply of operating fluid in the aforementioned apparatus is accomplished by using a pump that is driven by a driving motor of the vehicle, there are some cases in which the amount of ejection from the pump decreases and fails to provide a required fluid pressure when the operation speed of the driving motor decreases. In particular, when the transmission mechanism is operated to a neutral position by an operating person while the vehicle is running, the operation speed of the driving motor is controlled to the lowest value within a control range. In this occasion, problems occur. That is, the amount of operating fluid ejected from the pump and the pressure of operating fluid therefrom drop even though the vehicle is running.
The apparatus described in the aforementioned patent application, upon detecting a tendency of decreasing pressure of operating fluid supplied, closes the return side of a fluid pressure circuit to prevent reductions in the fluid pressure. However, provision of such a construction complicates the construction of the fluid pressure circuit, and leads to a problem of cost increase.
The invention has been accomplished in order to solve the aforementioned problem. It is an object of the invention to control the amount of ejection from a pump for supplying operating fluid to a drive power transfer mechanism to a value that allows the drive power transfer mechanism to operate during the running of a vehicle.
In order to achieve the aforementioned object, a vehicle drive apparatus in accordance with a mode of the invention controls an operation speed of a driving motor to a high operation speed that is higher than a control target value set for a stopped state of the vehicle if a power transfer apparatus is operated to a neutral state while the vehicle is in a running state. The high operation speed is an operation speed that allows a pump driven by the driving motor to produce an ejection pressure that makes it possible to operate the power transfer apparatus. Preferably, this operation speed is controlled to a minimum operation speed that is sufficient to operate the power transfer apparatus.
The aforementioned running state of the vehicle may be defined as a state in which the speed of the vehicle is greater than a speed at which it can be estimated that the vehicle has substantially stopped in speed shift operation of the power transfer apparatus. Specifically, the running state is a state in which the running speed is at least a vehicle speed at which it can be estimated that a speed ratio of the power transfer apparatus has been changed to a target speed ratio set for a stopped state by the shift operation.
Modes of the invention are not limited to the above-described vehicle drive apparatus. Other modes of the invention are, for example, a vehicle in which a vehicle drive apparatus in accordance with the invention is installed, a method of controlling the driving of the vehicle, etc.